1. Field of the Invention
This invention concerns an image decoding device and method for decoding, in target macro block units, coded image signals that are coded by DCT, quantization, and variable-length coding.
2. Description of the Related Art
In the field of image coding technology, a standard called MPEG4 is specified and standardized in the specifications titled, “ISO/IEC14496-2 Information Technology—Generic Coding of Audio-Visual Object.”
However, this document does not describe methods of implementing the decoding of image signals coded in accordance with MPEG4.
Also, though the book titled “MPEG-4 No Subete” (Japanese term meaning “All About MPEG4”; Miki et al, 1998, published by Kogyo Chosakai Publishing Co., Ltd.) provides a description of the principles of a decoding method for this type of coded signal, it does not provide specific methods of implementation. Besides the above, substantial literature concerning specific implementation methods could not be found.
Thus, a specific method of implementation is now considered. First as described in the abovementioned book, an entire image size is comprised by arranging areas of 16×16 pixels, called macro blocks, vertically and horizontally. Each macro block is associated with a total of six types of data, that is, the luminance values (Y1, Y2, Y3, and Y4) concerning the four blocks (each comprised of 8×8 pixels) at the upper left, upper right, lower left, and lower right and two color difference values (Cb and Cr). These data are processed in the order, Y1, Y2, Y3, Y4, Cb, and Cr.
With regard to the prediction process for decoding coded image signals, the abovementioned specifications do not indicate limits concerning the memory area to be used for the prediction process. Therefore, this memory area may be set freely.
The method of securing a memory area corresponding to the image size as the memory area to be used for the prediction process may thus be considered.